There are several ways of realizing standard ultrahigh frequency filters with mechanical elements. These filters may be LC cell filters, varactor filters or ultrahigh frequency filters with rods. All these elements allow high-performance ultrahigh frequency filters to be assembled, but are generally expensive.
There are other types of ultrahigh frequency filters realised using micro-electronic techniques on various substrates. The filters realized according to these techniques are easier to produce, but have inferior performances; moreover, their central frequencies cannot be easily phase-shifted, for example when aiming to produce a filter which is frequency responsive.
The technical problem to be solved is therefore to produce simply and inexpensively an adjustable and high performance ultrahigh frequency filter.